Existing anti-collision lights utilize Xenon flash tube technology. However, anti-collision lights using LEDs are advantageous because of their longer lives, lower power consumption, and reduced weight (because a separate power supply is not needed) compared to Xenon-based systems.
Also, in Xenon-based anti-collision lights, providing both visible and covert (infrared) capabilities generally causes the package size to grow. Such dual-mode capability causes the increase in size because infrared (IR) sources cannot be mounted in the same envelope as the Xenon flash tube.
FAR Requirements
The Federal Aviation Regulations (FAR) requirements for minimum effective intensities for an anti-collision light system are shown in FIGS. 6A and 6B. The FAR photometric requirements are rotationally symmetric about the vertical axis. Thus, for a given vertical angle above/below the horizontal plane of the aircraft, the minimum intensity required for each horizontal angle around the vertical axis is the same. As indicated by FIG. 6A, at a vertical angle of 0 degrees, the effective light intensity must be 400 effective candle power (ECP) for the entire 360-degree horizontal range (i.e., anywhere along the horizontal plane). The following Table 1 includes the minimum effective intensities specified by the FARs (as of the filing date of this application), as illustrated in FIG. 6B.
TABLE 1Angle Above/Below Horizontal PlaneEffective Intensity (ECP)0 to 5 degrees400 5 to 10 degrees24010 to 20 degrees8020 to 30 degrees4030 to 75 degrees20
It should be noted that flash characteristics are specified for anti-collision light systems by the FARs. (Specifically, the FAR specifications set a minimum and maximum effective flash frequency for the system). Thus, the effective intensity of an anti-collision light must be determined using the light's instantaneous intensity as a function of time, and flash duration.
For instance, the Blondel-Rey equation (provided below as Eq. 1) may be used to determine the effective, equivalent intensity of a flashing light compared to a light with a steady-state output. According to the Blondel-Rey equation:
                    Ie        =                                            ∫                              t                1                                            t                2                                      ⁢                                          I                ⁡                                  (                  t                  )                                            ⁢                                                          ⁢                              ⅆ                t                                                          0.2            +                          (                                                t                  2                                -                                  t                  1                                            )                                                          (                  Eq          .                                          ⁢          1                )            where:                Ie=effective candle power (ECP)        (t2−t1)=pulse duration in seconds, and        I(t)=instantaneous intensity as a function of time.        
The coverage illustrated by FIGS. 6A and 6B may be satisfied by multiple light installations, provided that each light meets the required photometric specification for it's respective area. Typically, each red fuselage anti-collision light will cover either the upper or lower portion of the specification, while the white anti-collision lights will cover specific horizontal sections (each wingtip anti-collision light will have 110-degree coverage, and the aft light will cover the remaining 140 degrees).
Considerations in Using LEDs
Red LEDs experience a much higher level of degradation when operated near their maximum allowable junction temperature. Thus, thermal management is important for LED systems, particularly ones using the AlInGaP technologies, which are typically used in red and amber LED's.
Also, it may be advantageous to use flashing LEDs in anti-collision lights to provide more conspicuity to the aircraft. However, synchronizing flashing anti-collision lights on an aircraft with wild frequency power presents certain challenges. Thus, it is a goal to provide synchronized anti-collision lights that flash at a stable rate when powered from a wild frequency bus.